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Difference between Turn Around Time (TAT) and Waiting Time (WT) in CPU Scheduling

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  • Difficulty Level : Medium
  • Last Updated : 04 Jul, 2022

In CPU Scheduling, we often need to find the average Turnaround and Waiting Time with the help of Arrival, Burst and Completion Time. Let’s have a brief look of them: Turnaround Time (TAT):

  1. It is the time interval from the time of submission of a process to the time of the completion of the process.
  2. The difference b/w Completion Time and Arrival Time is called Turnaround Time.

Completion Time (CT): This is the time when the process completes its execution. Arrival Time (AT): This is the time when the process has arrived in the ready state.

TAT = CT - AT

Waiting Time (WT):

  1. The time spent by a process waiting in the ready queue for getting the CPU.
  2. The time difference b/w Turnaround Time and Burst Time is called Waiting Time.

Burst Time (BT): This is the time required by the process for its execution.

WT = TAT - BT

Now with Waiting Time and Burst Time, we can also calculate Turn Around Time via:

TAT = BT + WT

Example:

ProcessBurst Time (in sec.)
P124
P23
P34

Solution: Figure – Gantt Chart

Avg. TAT = (24 + 27 + 31) / 3 = 27.33 sec
Avg. WT  = (0 + 24 + 27) / 3 = 17.0 sec 

Let’s see the difference between Turnaround Time and Waiting Time:

Turn Around TimeWaiting Time
The time since the process entered into ready queue for execution till the process completed it’s execution.The time process spent in the ready queue and for I/O completion.
Different CPU Scheduling algorithms produce different TAT for the same set of processes.CPU Scheduling Algorithm doesn’t affect the amount of time during which a process executes or does I/O but only the amount of time that a process spends waiting in the ready queue.
The turnaround time is generally limited by the speed of the output device.Waiting time has no such major effect.
Turn Around Time = Burst time + Waiting time. Waiting time = Turn Around – Burst time.
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